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Background. The physical processes governing flame behaviour are key elements for a better understanding of forest fires. Aims. To study the combustion properties of several dead Mediterranean forest fuels. Method. Samples of straw, eucalyptus, shrubs and Pinus Pinaster with the same load were placed in circular containers of the same size, and ignited in the absence of wind. Key results. The combustion parameters (burning rate, flame height, temperature and gas velocity) evolved according to the same trend regardless of the fuel type. A new law is proposed to account for the anomalous relaxation processes occurring in the growth and decay phases of the flame. The dynamic exponent depends on the vegetation type only in the growth phase (highest for Pinus Pinaster and lowest for straw). The relaxation times are shortest for shrubs and largest for straw. The maximum flame height and burning rate are largest for shrubs and lowest for straw. Froude modelling suggests that the scaling behaviour of the flame may depend on the fuel type. Conclusions. The observed relaxation parameters driving fire dynamics and the combustion characteristics depend on the nature of the fuel. Implications. Further investigation of the vegetation region's influence on these properties is necessary. [ABSTRACT FROM AUTHOR]

An approach to the mathematical modeling of the suppression of thermal decomposition and flaming combustion of forest fuels (FFs) is proposed which differs from the well-known approaches in that the pyrolyzed FF layer is represented as a heterogeneous structure with high porosity and the thermophysical characteristics of this layer are described using additive mathematical models of thermal conductivity, heat capacity, and density. Experimental studies of the main thermophysical characteristics (thermal conductivity, heat capacity, and thermal diffusivity) of typical FFs were performed. Mathematical modeling of heat- and mass-transfer processes under the above conditions was performed, and the suppression characteristics of the destruction reaction of a typical FF were determined using the values of thermophysical characteristics established in the experiments. The ranges of the integral characteristics of FF flame suppression with varying thermophysical characteristics of FFs within permissible limits were identified. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study of the initiation and containment of the flaming combustion and thermal decomposition of typical forest fuels by creating a fire break in the form of a wet layer of fixed width, length, and depth with a known volume of contained liquid. The ranges of parameter values that ensure stable suppression of the flaming combustion and thermal decomposition of forest fuel material were determined Experiments were performed for all major types of forest fuels: leaves, needles, branches, and mixtures thereof. The minimum water volumes and fire-break sizes required for guaranteed containment of combustion of the investigated forest fuels are predicted. [ABSTRACT FROM AUTHOR]

An experimental study has been performed to investigate the integral characteristics of the processes of heat and mass transfer and phase transformations during interaction of a droplet flow with the combustion front of a highly porous condensed material. The macroscopic regularities of the suppression of flaming combustion and thermal decomposition of typical forest fuel material due to the removal of heat as a result of its absorption during vaporization and convective cooling were studied. Three modes of interaction of a droplet aerosol with the burning forest fuel materials were considered. The time of combustion termination and the time of thermal decomposition of forest fuel materials were determined. The mechanisms of the main physicochemical processes occurring during interaction of droplet flow with the combustion front of typical forest fuel materials were established. [ABSTRACT FROM AUTHOR]

Single particle combustion behaviours of coal-biomass fuel mixtures are studied. Different biomass i.e. sawdust, wood and rice husk is blended with locally available low grade coal to carry out the experimental investigation. The combustion of solid fuel consists of flaming combustion and char combustion. Rice husk showed higher flaming time and char glowing time because of higher ash and particle density. The burning time of coal-rice husk mixture fuel sample is higher compared to other samples due to the combine effect of particle density and ash content of the fuel samples. Ignition mass flux of saw dust is higher compared to rice husk and wood fuel particles because of the presence of higher volatiles in sawdust. The diameter index for flaming combustion, char combustion are 1.13 to 0.47 and 0.63 to 1.23 respectively for 0%–40% coal in coal/wood fuel mixtures. It is observed that with the increases in surface area/volume ratio, flaming and char combustion decreases due to reduction in effective surface area of the particle for combustion. This study concludes that particle size or surface area/volume together with particle density are the primary controlling parameter for better conversion of fuel mixtures in any co-combustion system. • Single particle combustion studies of coal/biomass fuel mixtures. • Ignition mass flux of saw dust is higher compared to rice husk and wood. • Diameter index for flaming and char combustion are 1.13 to 0.47 and 0.63 to 1.23 • Increases in surface area/volume ratio decrease the flaming and char combustio n. [ABSTRACT FROM AUTHOR]